As one step in the flexographic printing process, printing plates are developed. During the development process, the plates are washed by a solution of solvents, typically comprising about 95% perchloroethylene (tetrachloroethylene) and about 5% butyl alcohol, although these proportions can vary for a particular application. The solvents are used in wash away areas of a polymer artificial rubber printing plate so that the desired pattern to be printed remains. The dissolved printing plate material, a polymer, goes into the solution. The washed plate is then heated in an oven in the next stage of processing.
The cleaning process requires a relatively pure solvent solution. However, the dissolved polymer material from the printing plate that is washed off by the solvent builds up in concentration in the solution, eventually contaminating the solution. As the concentration of material increases, the plates become tacky and require hand cleaning, a time consuming task. Also, the dissolved material will come out of solution and build on the surfaces in the solvent flow path.
Because of the build up on this material, the solvent must be replaced relatively frequently. Because the dissolved polymer has been classified as a hazardous material, the used solution can not be readily disposed of. Typically, the user will either pay a service to take the used solution and separate the solution and the dissolved polymer material by a distillation process or buy the expensive distillation equipment to distill the solution on site. while the distillation process separates the polymer material from the solution, it also disturbs the balance of chemicals. Thus, the concentration of perchloroethylene and alcohol must be measured after distillation, and a suitable quantity of the proper chemical added to rebalance the solution. Because of the inconvenience and expense related to this process, a need exists for a better technique to separate dissolved materials, such as polymers, from the solution without altering the solution itself.